The pUL37 tegument protein guides alpha-herpesvirus retrograde axonal transport to promote neuroinvasion

Abstract

A hallmark property of the neurotropic alpha-herpesvirinae is the dissemination of infection to sensory and autonomic ganglia of the peripheral nervous system following an initial exposure at mucosal surfaces. The peripheral ganglia serve as the latent virus reservoir and the source of recurrent infections such as cold sores (herpes simplex virus type I) and shingles (varicella zoster virus). However, the means by which these viruses routinely invade the nervous system is not fully understood. We report that an internal virion component, the pUL37 tegument protein, has a surface region that is an essential neuroinvasion effector. Mutation of this region rendered herpes simplex virus type 1 (HSV-1) and pseudorabies virus (PRV) incapable of spreading by retrograde axonal transport to peripheral ganglia both in culture and animals. By monitoring the axonal transport of individual viral particles by time-lapse fluorescence microscopy, the mutant viruses were determined to lack the characteristic sustained intracellular capsid motion along microtubules that normally traffics capsids to the neural soma. Consistent with the axonal transport deficit, the mutant viruses did not reach sites of latency in peripheral ganglia, and were avirulent. Despite this, viral propagation in peripheral tissues and in cultured epithelial cell lines remained robust. Selective elimination of retrograde delivery to the nervous system has long been sought after as a means to develop vaccines against these ubiquitous, and sometimes devastating viruses. In support of this potential, we find that HSV-1 and PRV mutated in the effector region of pUL37 evoked effective vaccination against subsequent nervous system challenges and encephalitic disease. These findings demonstrate that retrograde axonal transport of the herpesviruses occurs by a virus-directed mechanism that operates by coordinating opposing microtubule motors to favor sustained retrograde delivery of the virus to the peripheral ganglia. The ability to selectively eliminate the retrograde axonal transport mechanism from these viruses will be useful in trans-synaptic mapping studies of the mammalian nervous system, and affords a new vaccination paradigm for human and veterinary neurotropic herpesviruses.

The Carboxyl Terminus of Tegument Protein pUL21 Contributes to Pseudorabies Virus Neuroinvasion

“…Previous studies on the inner tegument proteins VP1/2 (pUL36) and pUL37 revealed that both proteins are critical for alphaherpesvirus retrograde axonal transport and neuroinvasion (6,65,66). Our findings in this study provide evidence that pUL21, as an inner tegument protein like VP1/2 and pUL37, also has a potential role in PRV retrograde axonal transport and neuroinvasion.…”

The herpes simplex virus type I deamidase enhances propagation but is dispensable for retrograde axonal transport into the nervous system

“…The pUL36 large tegument protein promotes transmission from epithelial tissues to nerve endings and subsequently tethers capsids delivered into the cytosol of axon terminals to the dynein/dynactin microtubule motor complex to drive retrograde axonal transport to sensory ganglia (12, 18). The pUL37 tegument protein sustains dynein-based microtubule transport by restraining opposing plus-end motion (22). Consistent with these roles, pUL36 and pUL37 remain attached to capsids upon entry into cells (2, 3, 5, 26), with pUL36 bound directly to the capsid surface (7, 9, 27, 28) and pUL37 bound to pUL36 (10, 11, 29) such that pUL36 tethers pUL37 to the capsid (13).…”

“…Of these enzymes, only the pUL36 deubiquitinase is reported to contribute to the neuroinvasive property of these viruses (18, 19). Nevertheless, pUL37 is a critical component of the neuroinvasive apparatus (20), with an amino-terminal region essential for the delivery of incoming capsids to the neural soma by sustaining dynein-based microtubule transport in axons (21, 22).…”

Characteristics of herpes simplex virus infection and pathogenesis suggest a strategy for vaccine development

“…On the basis of data from studies of HSV pathogenesis, this conclusion is reasonable. The only uncertainty is whether viral latency, which depends on the process of viral entry into neurons from epithelial tissue, might lose control of the activated innate immune response during viral infection or still retain control because of the strong neurotropic characteristic of HSV . Although there are many examples of neurotropic viruses that have the characteristics of intense neurotropism and a shorter proliferative cycle than HSV, a lower rate of neuron infection was observed for these viruses than for HSV .…”